Air Gun Home :: View topic - Some questions for my mental clairification

donec · Senior Member

1. If I am thinking correctly if you use 2 different weight pellets in the same gun and under the same conditions then the lighter pellet should give a higher velocity than the heavy one.

2. Now assuming this is the case would you excpect a .17 pellet weighing 7.9 gr to have a higher velocity than a .22 pellet weighing 10.6 gr when both pellets were fired under the same conditions and from the same make of gun just different cal?

3. Do you get less shots from a pcp when firing heavy pellets than when firing light pellets?

4. Do you get less shots from a co2 when firing heavy pellets than when firing light pellets?

5. Do you get less shots in the larger cal guns than lower cal guns using the same pressure?

I read this to my wife and her comment was "you will make people crazy" and it kind of sounds like I might, but I have been reading and researching till my head is spinning. I hope this doesn't sound too crazy.

creeper · New Member

The fit of the pellet can enter into it. For example, .177 CP 10.65s, which are a tight fit in any of my .177 guns, will shoot as much as 60fps slower than a looser fitting pellet, say an H&N 10.65.

Can't help you with the rest...

C

fritz · Silver Status Member

1. Yes. lighter = faster

2. Yes, but the larger diameter pellet will likely carry more energy because it is more efficient.

3. No. You get the same amount of shots. The heavier pellets, again are *usually* more efficient, so you send more energy downrange every fill with the heavier (usually).

4. See No. 3.

5. You get what the gun is set to release. IE. I take a .17 Disco and it is tuned to shoot 8gr pellets at 900fps. This equals roughly 14.4fpe. It shoots full power for 20 useable shots (288fpe/fill). Now I change the barrel out and it shoots .22 (14.3gr) at 800fps for 20.32fpe. It still gets 20 shots, but releases 406.4fpe/fill.

It has been explained to me that the larger (.22) has more surface area in the skirt to receive energy from the air, so it may not go faster because of the weight. It is still carrying more energy than the smaller pellet. Of course some pellet designs may counter this. There are a million other factors that contribute to this, but the stated are most prevailing.

fritz · Silver Status Member

Go to the "Rifles" section. Read up on all of Rsterne's posts about his modifications. Usually there are many colorful graphs to look at, too. For example, what I got out of his .25 Disco post was that the .22 shot about 52fpe while the .25 shot 58fpe. This shows that the .25 is generally more efficient, but may not be the only factor involved.

Slavia · Moderator

I would say #1 is yes, based on my own experience.

I would also say #2 is yes, simply because the dual barrel guns usually advertise different speeds for the different calibers.

While I can't answer the rest, I do have another question: Is the "valve dump" of a CO2/pneumatic gun independent of the situation downstream in the bore? Are source pressure, hammer spring tension, valve spring tension, hammer mass, and valve mass the only things that determine how much gas gets dumped, or are there other factors?

fritz · Silver Status Member

I'm not crazy, my guns are. Shocked

donec · Senior Member

Thanks all for the replies.

The fit of the pellet is something I don't consider since I am theoretically assuming perfect pellets.

I understand that the heavier weighted pellet will carry more energy but at this point I am not concerned with energy just trying to understand. I shoot paper, balloons, clay pigeons, cans and other stuff but mostly paper for testing my skill. shooting these do not require much in energy. Wouldn't it be correct to say accuracy without the need for energy as is best served up with a flat trajectory and enough weight to handle any wind along with a good aim?

It's those million other factors that have my brain spinning and so the questions are trying to be simplistic and ignore those factors for the time being.

Rsterne's posts make my head burst and seem to pose more questions I am not yet ready to consider.

fritz · Silver Status Member

I don't usually find BB's fun, except in my repeater pistol. Very fun to pop cans, about 20 shots in the magazine.

If it will reach the target, anything works fine for paper. Wind can be bucked by pellets with more energy, their momentum resists the wind. What distance do you usually shoot at?

sniper · Silver Status Member

hmmm good thread. with pcp/multi-pump. what i know is that heavier pellets yield higher energy because of the valve staying open longer. the heavier pellet is coming out slower there for the valve is opened slightly longer yielding a little more air usage?? that was an answer and question.

my .22 mrod with throw 21 grain kodiaks at 800 fps
but only throw 14.3's at 900-same pressure.

my power modded 392 is the same. 850/14.3 but 750.kodiaks Shocked

and.... 640/28.4 ej's.

i don't know if that was much of an answer. Rolling Eyes

yeah bob can figure it all out. Laughing

you're not crazy. all the wives just need a support group..

rsterne · Moderator

1. If you are talking the same caliber, then lighter pellets are generally faster, other than how that is altered by barrel fit and friction....

2. Once you are taking different calibers, not necessarily so if the pellets are close to the same weight.... as the larger caliber pellet has a bigger base area for the air to push on.... accelerating it faster.... As an example, in tests of a Beeman R1 (HW80) Straight Shooters clocked an 11.5 gr. Silver Arrrow in .177 at 761 fps, a 13 gr. Crow Magnum in .20 cal at 758 fps, and a 14 gr. MeisterKugeln in .22 cal at 769 fps....

3. You actually tend to get a few MORE shots when firing heavy pellets in a PCP as they operate more efficiently.... The heavier pellet gets a longer sustained "push" from the same valve and pressure.... and actually uses slightly less air per shot because the "back pressure" it creates allows the valve to shut without wasting as much air.... hence more shots per fill (maybe only 10%)....

4. The same can occur with CO2.... especially in a loud gun like a 2240 where there is a lot of gas being wasted.... Same arguments as above (again, only a small difference)....

5. This is a bit trickier.... If the pellet weight is the same, you would get slightly fewer shots in the larger caliber because the pellet will leave the barrel at a higher velocity.... less time in the barrel, less backpressure, more wasted air....

These are the results I have seen in actual testing and documenting shot strings.... and then trying to figure out the "why" after I know the "what"....

Bob

donec · Senior Member

fritz · Silver Status Member

What exactly are you trying to figure out?

donec · Senior Member

fritz · Silver Status Member

Regardless of impact energy, the more power you're sending downrange, the less it should be affected. Pellets moving slower, but with a much higher BC should actually shoot "flat" for a much longer distance.

Question for Roger: Projectile drop is not a function of velocity, but a function of gravity (9.8m/s/s drop) and flight time?

Lipoly · Veteran Member